1. Field of the Invention
The present invention relates to a fluid delivery device for accurately delivering fluid little by little.
2. Description of the Conventional Art
Recently, in order to inject liquid medicine into human's body with accuracy, various types of infusion pumps are used.
The conventional infusion pumps are classified into 4 types, which are a syringe pump, peristaltic (rotor type) pump, finger pump and bellows pump. Except for the bellows pump, each of the above infusion pumps is provided with a stepping motor, rotary solenoid motor or DC motor so that liquid medicine can be delivered by a drive force generated by the motor. Accordingly, since a complicated control mechanism is adopted to control an infuse volume of the liquid medicine, the weights and dimensions of these pumps are usually large and further their cost is expensive. Therefore, it is common that these pumps are used beside the bed in a hospital, and they are not suitable for portable or disposable use. In the bellows pump, vaporization pressure of freon gas is utilized, and liquid medicine is delivered by the action of vaporization pressure. However, it is difficult to control the vaporization pressure of freon gas. Especially when a very small amount of liquid medicine is injected over a long period of time, the accuracy of the injection is difficult to maintain.
One of the present inventors made an application for a patent of the apparatus having a pumping function where the rate of gas flow is controlled with an electrochemical cell in which gas is generated when a direct current is made to flow (Unexamined Japanese Patent Publication No. Sho. 58-48209). Recently, an electrochemically driven drug dispenser has been proposed, in which the aforementioned principle is adopted. In this system, liquid medicine is delivered by the action of gas generated in proportion to a quantity of electricity when a direct current is made to flow in the electrochemical cell part. According to the invention proposed by H. J. R. Maget disclosed in U.S. Pat. Nos. 4,687,423, 4,886,514 and 4,902,278, the electrochemical cell is composed of a polymer electrolyte membrane and a pair of electrodes attached onto both sides of the electrolyte membrane. In this cell, when a current is allowed to flow between both electrodes so that an electrochemical active mass is supplied to the first electrode, the electrochemical active mass is ionized there, and the generated ions move through the electrolyte membrane and arrive at the second electrode. At the second electrode, ions are converted into a pressurized gas, which is used as a drive source for pushing the diaphragm. When hydrogen is used as the electrochemical active mass, hydrogen functions as the pressurized gas. On the other hand, when oxygen and air are used as the electrochemical active mass, oxygen functions as the pressurized gas.
However, in the drug dispenser disclosed in U.S. Pat. No. 4,687,423, gas is pressurized by the electrochemical cell, and is released through a pump valve when its pressure is increased to a predetermined value. By the action of this gas pressure, a flexible diaphragm is subjected to pulsation so that the liquid medicine in a pump chamber is delivered. When this drug dispenser is operated, a current is made to flow in a predetermined direction, however, it is necessary to accurately adjust a relation between the pressure required for expanding and contracting the flexible diaphragm including a part of the wall of the pump chamber and the pressure required for operating a pump valve of the pressure release mechanism. Further, the electrochemical cell, pump chamber and pressure release mechanism are integrated into one unit. Therefore, when different types of medicines are used, the pump chamber must be washed each time. Further, the structure of the apparatus is considerably complicated. As a result, the cost of the apparatus is increased. Therefore, it is impossible to put the pump into disposable use.
In the drug dispenser described in U.S. Pat. No. 4,886,514, the electrochemical pump and liquid medicine container are integrated into one unit in which a flexible diaphragm, bellows or sliding wall provided for separating the electrochemical pump from the liquid medicine container is deformed or moved so that the medicine in the medicine container can be delivered. In this drug dispenser, since the electrochemical pump and medicine container are integrated into one unit, they can not be separated from each other. Accordingly, it is difficult to put this apparatus in disposable use. Further, this apparatus also has some disadvantages such that the medicine container must be washed each time when different types of liquid medicines are used.
In the fluid delivery pump described in U.S. Pat. No. 4,902,278, a prime mover portion in which the power supply part and electrochemical cell part are integrated into one unit can be separated from the fluid reservoir part, and a flexible membrane of the fluid reservoir part is pushed by the gas generated from the prime mover part so that the fluid can be delivered. However, the structure of the fluid reservoir part of this apparatus is complicated. Therefore, the fluid reservoir part is not suitable for disposable use. Further, it is complicated to put liquid medicine into the fluid reservoir part.
For a remodeled pump of this electrochemical liquid transporting pump, there is provided a method in which electrolysis of water is used (Unexamined Japanese Patent Publication No. Hei. 2-302264). According to this method, an electrochemical cell is used in which a cathode is integrally joined on one side of an ion exchange membrane and an anode is integrally joined on the other side of the ion exchange membrane. Alternatively, an electrochemical cell is used in which a cathode and anode are integrally joined on one side of an ion exchange membrane under the condition that the cathode and anode are separated from each other so that they can be insulated. Water is contained in the above electrochemical cell, and a direct current is made to flow in both electrodes so that hydrogen and oxygen are generated by the electrolysis of water. Generated hydrogen or oxygen, or alternatively mixture gas of hydrogen and oxygen is used for the pressure source of the liquid infusion pump.